The following terms and concepts are used in 
D6 Dungeons.

Action

An action is a single thing a character does. It could be something they do in battle, like attacking a goblin with a sword or outside of combat, like gathering information from a lively tavern. In D6 Dungeons, the players roll dice determined by their skills to see if their characters succeed on challenges.

Challenge

A challenge could be anything the characters face during a story, from a pack of snarling wolves to a raging river in their path. What they choose to do is up to the players, but whether or not their actions are successful is up to the dice.

Character

The players take the role of heroes, powerful and dynamic people at the center of every story.

Class

A class is a character's role or adventuring profession. It determines what the character is good at with a selection of four class skills. It also sets the character's starting equipment.

Dice

D6 Dungeons requires a handful of six-sided dice to play. A single die is sometimes called a d6, while rolling three dice would be noted as 3d6. The dice are used to determine the success or failure of most actions, or challenges, the characters take.

Narrator

The narrator is the storyteller and referee, responsible for not only telling the story but making sure the rules are followed wherever appropriate. It is the narrator's job to make the game interesting and challenging.

Scene

D6 Dungeons is broken up into scenes, which work a lot like they do in movies and television. There's no set size or duration of a scene; they are as large and take as long as they need to move the story along. A scene might be a thirty second barroom brawl, an hour-long audience with the king, or even a two-week hike through a snowy mountain pass. Some of the actions a player can take affect them or their surroundings for an entire scene. Casting a protection spell could last for the entire barroom brawl, using diplomacy could get the king to look favorably on them during their interaction, and one roll to see how effectively they navigate the mountains is good enough for that entire scene. The narrator decides what goes into a scene, where it takes place, how long it lasts, and what the specific challenges and potential rewards are, then it's up to the players to figure out how they approach it.

Skill

Skills are usually very broad, covering a wide range of situations that are all somewhat related. A class skill is one of the four standard skills provided by a character's class.